1. Field of the Invention.
The present invention relates in general to radio frequency (RF) antennas, and, in particular, to dynamically optimizing the performance of a circularly polarized antenna.
2. Description of the Related Art.
The use of RF electronics has become commonplace in many facets of modem living, e.g., cellular telephones, satellite communications, television reception, computers, etc. Many of today""s RF signals are transmitted in a wireless fashion, which requires the use of transmitting and receiving antennas to perform such tasks.
As many RF devices become smaller, antenna design has become very important because of the antenna""s important role in the communications link. Without a properly tuned antenna, or an antenna that properly uses the gain properties associated with such an antenna, the communications link can be lost or unreliable, making the RF electronic device unusable in certain situations. Many small RF devices use patch antennas because of their small size and ease of integration for packaging of the RF device. For satellite signal reception, e.g., Global Positioning System (GPS) satellite signals, circularly polarized patch antennas are used extensively.
Even with the attractiveness of the patch antenna size and ease of integration, there remain a number of difficulties with the implementation of these antennas. The small size of the patch antenna is typically achieved by making the patch antennas thin and increasing the dielectric constant of the dielectric material between the upper and lower plates of the antenna. However, as the antenna shrinks in size, the bandwidth of the antenna decreases. With narrower bandwidth antennas, precise tuning of the antennas becomes necessary, or the antenna will not be able to receive or transmit the signal of interest.
Patch antennas, because of their thin nature, material makeup, and small size, are also more susceptible to changes in surrounding environment than other types of antennas. Patch antennas can be mistuned by nearby plastics, metal, and even the near proximity of the user.
As such, environmental effects, such as mistuning and bandwidth narrowing, can seriously degrade the performance of the antenna, and make implementing designs in a low cost product very difficult. It is often necessary to have antenna manufacturers tune the antennas for a specific product, and the yield of this tuning may still cause a large amount of unit-to-unit variation. It is desirable to be able to tune each antenna after placement into the device if possible to allow for manufacturing tolerances in the antenna and the housing to be compensated for. Further, once the antenna has been installed and the RF electronic device delivered to a user, the antenna should be tunable by the user to compensate for other environmental effects not seen at the manufacturer""s facility.
Tuned antennas, and methods of tuning antennas exist in the literature. U.S. Pat. Nos. 5,943,016, 6,005,519, and 6,061,025, which are all incorporated by reference herein, describe methods to tune the antenna by adding to the metal areas of the patch. Such an approach would not be acceptable for antennas that have already been installed in a device. U.S. Pat. No. 5,777,581, which is incorporated by reference herein, describes a method, such as described above, but the metal areas to be added are done so through switching diodes, which allows for dynamic changes in the electric field. U.S. Pat. No. 4,529,980, which is incorporated herein by reference, describes using varactor diodes to tune a linear antenna. Such methods are not acceptable or directly applicable to conveniently tune a circularly polarized patch antenna.
It can be seen, then, that there is a need in the art for a method and apparatus to easily tune the antenna to allow for greater antenna manufacturing tolerances. It can also be seen that there is a need in the art for a method and apparatus to compensate for variations in the antenna caused by the physical properties of the application using the antenna. It can also be seen that there is a need in the art for a method and apparatus that can accomplish, to the extent possible, both tuning the antenna to allow for greater manufacturing tolerances, and compensation for variations caused by the physical properties of the application using the antenna. It can also be seen that there is a need in the art for a method and apparatus that can compensate for variations after the antenna is installed in the housing of the intended application. It can also be seen that there is a need in the art for optimizing the antenna performance and reduce or eliminate the variations in performance after deployment of the RF device.
To minimize the limitations in the prior art, and to minimize other limitations that will become apparent upon reading and understanding the present specification, the present invention discloses a method and apparatus for a method to be able to dynamically tune a circularly polarized patch so that when installing the antenna during the manufacture of an assembly, and in the field, the unit can optimize the antenna performance and reduce or eliminate the variations in performance.
An apparatus in accordance with the present invention comprises a first varactor and a second varactor. The first varactor has a first terminal that is coupled to the metal patch of the circularly polarized patch antenna at a first point and has a second terminal that is coupled to ground. The second varactor has a first terminal that is coupled to the metal patch of the circularly polarized patch antenna at a second point and has a second terminal that is coupled to ground. Application of a varying DC voltage to the pin of the circularly polarized patch antenna tunes the first varactor and the second varactor coupled to the circularly polarized patch antenna, and hence tunes the antenna as installed.
It is an object of the present invention to provide a method and apparatus to easily tune the antenna to allow for greater antenna manufacturing tolerances. It is an object of the present invention to provide a method and apparatus to compensate for variations in the antenna caused by the physical properties of the application using the antenna. It is an object of the present invention to provide a method and apparatus that can accomplish, to the extent possible, both tuning the antenna to allow for greater manufacturing tolerances, and compensation for variations caused by the physical properties of the application using the antenna. It is an object of the present invention to provide a method and apparatus that can compensate for variations after the antenna is installed in the housing of the intended application. It is an object of the present invention to optimize the antenna performance and reduce or eliminate the variations in performance after deployment of the RF device.